The present invention is directed to a flexographic printing apparatus, and more particularly to a flexographic printing apparatus having an electric charging unit to enhance print quality.
A conventional flexographic printing press is typically provided with a plurality of printing stations, each of which prints a moving web with an image in a respective color. Each of the printing stations is provided with a rotating cylindrical ink roller, also referred to as an xe2x80x9caniloxxe2x80x9d roller, having a regular pattern of minute recesses or ink cells formed therein. Ink is applied to the ink roller by submerging at least a portion of the ink roller in an ink reservoir, or by applying ink to a portion of the ink roller via an ink applicator.
A flexographic press has a rotating cylindrical printing roller disposed adjacent the ink roller. The printing roller has a printing plate mounted thereon. The printing plate may be held in place on the printing roller by an adhesive layer, such as adhesive tape, disposed between the printing plate and the printing roller. The printing plate is composed of a photosensitive material that is subjected to a photo-etching process to form raised portions on the printing plate which correspond to a desired image to be printed. The printing roller is disposed adjacent the ink roller so that ink is transferred from the ink cells in the ink roller to the raised areas on the printing plate.
U.S. Pat. No. 4,697,514 to George, et al. discloses a gravure printing apparatus having a gravure cylinder that is disposed partially within an ink reservoir, a backing roller disposed adjacent the gravure cylinder, and an apparatus for applying a voltage to the backing roller. As shown in FIG. 7 of the George, et al. patent and described in connection therewith, the application of the voltage to the backing roller causes ink within the ink cells to rise above the surface of the gravure cylinder in order to enhance the ink transfer from the gravure cylinder to a paper web being printed.
In one aspect, the invention is directed to a flexographic printing apparatus for printing a moving web. The printing apparatus has a rotatable ink roller, a roller support that rotatably supports the ink roller, an ink source associated with the ink roller which provides ink for the ink roller, a rotatable printing roller associated with the ink roller, and a printing plate disposed on the printing roller that makes physical contact with the ink roller so that ink is transferred from the ink roller to the printing plate as the ink roller and the printing roller rotate.
The printing apparatus also has a rotatable backing roller disposed adjacent the printing roller so that the moving web on which ink is to be applied passes between the backing roller and the printing plate as the backing roller and the printing roller rotate so that a printed image is applied to the web. The apparatus also has a charge applicator that causes an electric charge to be applied to the printing plate.
The printing plate may be composed of a semi-conductive printing layer having an image-forming surface. The semi-conductive printing layer may have a resistivity in the range between about 50 thousand ohms per cubic centimeter and about 1.5 megohms per cubic centimeter. The printing layer may be a photo-sensitive polymer doped with conductive particles, and may have a resistivity in the range between about 100 thousand ohms per cubic centimeter and about one megohm per cubic centimeter. The charge applicator may be provided in the form of an elongate charge bar having a plurality of charging electrodes spaced from the printing roller. Alternatively, the charge applicator may make direct physical contact with a portion of the printing plate or the roller on which the printing plate is supported.
The printing apparatus may also have an insulating layer disposed between a semi-conductive printing layer and the printing roller. The insulating layer may have a resistivity of greater than about two megohms per cubic centimeter. The insulating layer may be provided in the form of an adhesive layer disposed between the printing layer and the printing roller.
The printing apparatus may also have a conductive layer disposed adjacent the semi-conductive printing layer, the conductive layer having a resistivity lower than about 50 thousand ohms per cubic centimeter, and a high voltage may be applied directly to the conductive layer in order to impart an electric charge to the semi-conductive printing layer.
The invention is also directed to a printing structure for a flexographic printing apparatus having a rotatable ink roller, a roller support that rotatably supports the ink roller, an ink source associated with the ink roller which provides ink to be applied to the ink roller, a rotatable printing roller associated with the ink roller, and a rotatable backing roller disposed adjacent the printing roller.
The printing structure has a semi-conductive printing layer adapted to be disposed on a printing roller. The semi-conductive printing layer is composed of a photo-sensitive polymer material having a resistivity in the range between about 50 thousand ohms per cubic centimeter and about 1.5 megohms per cubic centimeter. The semi-conductive printing layer has an image-forming surface having a plurality of raised areas corresponding to an image to be printed.
The semi-conductive printing layer may have a thickness of less than about one-fourth of an inch, and the semi-conductive printing layer may have a resistivity in the range between about 100 thousand ohms per cubic centimeter and about one megohm per cubic centimeter. The resistivity of the semi-conductive printing layer may be due to the presence of conductive particles therein. The printing structure may have an insulating layer disposed adjacent the semi-conductive printing layer, with the insulating layer having a resistivity of greater than about 100 megohms per cubic centimeter. The printing structure may also have a conductive layer disposed adjacent the semi-conductive printing layer, with the conductive layer having a resistivity lower than about 50 thousand ohms per cubic centimeter.
In a second aspect, the invention is directed to a flexographic printing apparatus for printing a moving web that comprises a rotatable ink roller, a roller support that rotatably supports the ink roller, an ink source associated with the ink roller that provides ink to be applied to the ink roller, a rotatable printing roller associated with the ink roller, and a printing plate disposed on the printing roller that makes physical contact with the ink roller so that ink is transferred from the ink roller to the printing plate as the ink roller and the printing roller rotate. The printing plate comprises a semi-conductive printing layer having an image-forming surface and a resistivity in the range between about 50 thousand ohms per cubic centimeter and about 1.5 megohms per cubic centimeter and an insulating layer disposed between the semi-conductive layer and the printing roller, the insulating layer having a resistivity of greater than about two megohms per cubic centimeter. The apparatus also includes a rotatable backing roller disposed adjacent the printing roller so that the moving web on which ink is to be applied passes between the backing roller and the printing plate as the backing roller and the printing roller rotate so that a printed image is applied to the web and a charge applicator associated with the printing roller that causes an electric charge to be applied to the semi-conductive printing plate.
In the invention in accordance with the second aspect, the charge applicator may comprise an elongate charge bar having a plurality of charging electrodes spaced from the printing roller; the charge applicator may make physical contact with a portion of the printing plate; the insulating layer of the printing plate may comprise an insulating sleeve; the insulating layer of the printing plate may comprise a fiberglass sleeve; the semi-conductive printing layer may comprises a photo-sensitive polymer doped with conductive particles; and the semi-conductive printing layer may have a resistivity in the range between about 100 thousand ohms per cubic centimeter and about one megohm per cubic centimeter.
In a third aspect, the invention is directed to a flexographic printing apparatus for printing a moving web that comprises a rotatable ink roller, a roller support that rotatably supports the ink roller, an ink source associated with the ink roller that provides ink to be applied to the ink roller, a rotatable printing roller associated with the ink roller, a printing plate disposed on the printing roller, the printing plate having an image-forming surface and making physical contact with the ink roller so that ink is transferred from the ink roller to the printing plate as the ink roller and the printing roller rotate, a rotatable backing roller disposed adjacent the printing roller so that the moving web on which ink is to be applied passes between the backing roller and the printing plate as the backing roller and the printing roller rotate so that a printed image is applied to the web, and a charge applicator associated with the printing roller that causes an electric charge to be applied to the printing plate.
In the invention in accordance with the third aspect, the printing plate may comprise a photo-sensitive polymer doped with conductive particles; the charge applicator may comprise an elongate charge bar having a plurality of charging electrodes spaced from the printing roller; the charge applicator may make physical contact with a portion of the printing plate; and the adhesive layer may be disposed between the printing plate and the printing roller.
In a fourth aspect, the invention is directed to a flexographic printing apparatus for printing a moving web comprising a rotatable ink roller, a roller support that rotatably supports the ink roller, an ink source associated with the ink roller and providing ink to be applied to the ink roller, a rotatable printing roller associated with the ink roller, and a printing structure disposed on the printing roller that makes physical contact with the ink roller so that ink is transferred from the ink roller to the printing structure as the ink roller and the printing roller rotate. The printing structure comprises a semi-conductive printing layer having an image-forming surface and a resistivity in the range between about 50 thousand ohms per cubic centimeter and about 1.5 megohms per cubic centimeter, a conductive layer disposed adjacent the semi-conductive printing layer and having a resistivity lower than about 50 thousand ohms per cubic centimeter, and an insulating layer disposed between the conductive layer and the printing roller, the insulating layer having a resistivity of greater than about two megohms per cubic centimeter. The apparatus also includes a rotatable backing roller disposed adjacent the printing roller so that the moving web on which ink is to be applied passes between the backing roller and the printing structure as the backing roller and the printing roller rotate so that a printed image is applied to the web and a charge applicator associated with the printing roller that causes an electric charge to be applied to the semi-conductive printing layer.
In the invention in accordance with the fourth aspect, the semi-conductive printing layer may have a resistivity in the range between about 100 thousand ohms per cubic centimeter and about one megohm per cubic centimeter, and the charge applicator may make physical contact with a portion of the conductive layer of the printing structure.
In a fifth aspect, the invention is directed to a printing structure for a flexographic printing apparatus having a rotatable ink roller, a roller support that rotatably supports the ink roller, an ink source associated with the ink roller which provides ink to be applied to the ink roller, a rotatable printing roller associated with the ink roller, and a rotatable backing roller disposed adjacent the printing roller. The printing structure comprises a semi-conductive printing layer adapted to be disposed on a printing roller, the semi-conductive printing layer comprising a photo-sensitive polymer material having a resistivity in the range between about 50 thousand ohms per cubic centimeter and about 1.5 megohms per cubic centimeter, and an image-forming surface on the photo-sensitive polymer material that has a plurality of raised areas corresponding to an image to be printed.
In the invention in accordance with the fifth aspect, the semi-conductive printing layer may have a thickness of less than about one-fourth of an inch, and the semi-conductive printing layer may have a resistivity in the range between about 100 thousand ohms per cubic centimeter and about one megohm per cubic centimeter.
In a sixth aspect, the invention is directed to a printing structure for a flexographic printing apparatus having a rotatable ink roller, a roller support that rotatably supports the ink roller, an ink source associated with the ink roller which provides ink to be applied to the ink roller, a rotatable printing roller associated with the ink roller, and a rotatable backing roller disposed adjacent the printing roller. The printing structure comprises a semi-conductive printing layer adapted to be disposed on a printing roller. The semi-conductive printing layer comprises a photo-sensitive polymer material having a resistivity in the range between about 50 thousand ohms per cubic centimeter and about 1.5 megohms per cubic centimeter and an image-forming surface on the photo-sensitive polymer material that has a plurality of raised areas corresponding to an image to be printed. The printing structure also comprises an insulating layer disposed adjacent the semi-conductive printing layer that has a resistivity of greater than about two megohms per cubic centimeter.
In the invention in accordance with the sixth aspect, the photo-sensitive polymer material may have a concentration of conductive particles dispersed therein to provide the semi-conductive printing layer with a resistivity in the range between about 50 thousand ohms per cubic centimeter and about 1.5 megohms per cubic centimeter; the insulating layer may comprise an insulating sleeve; the insulating layer may comprise a fiberglass sleeve; the printing structure may have a thickness of less than about one-fourth of an inch; and the semi-conductive printing layer may have a resistivity in the range between about 100 thousand ohms per cubic centimeter and about one megohm per cubic centimeter.
In a seventh aspect, the invention is directed to a printing structure for a flexographic printing apparatus having a rotatable ink roller, a roller support that rotatably supports the ink roller, an ink source associated with the ink roller which provides ink to be applied to the ink roller, a rotatable printing roller associated with the ink roller, and a rotatable backing roller disposed adjacent the printing roller. The printing structure comprises a semi-conductive printing layer adapted to be disposed on a printing roller. The semi-conductive printing layer comprises a photo-sensitive polymer material having a resistivity in the range between about 50 thousand ohms per cubic centimeter and about 1.5 megohms per cubic centimeter and an image-forming surface on the photo-sensitive polymer material that has a plurality of raised areas corresponding to an image to be printed. The printing structure also comprises a conductive layer disposed adjacent the semi-conductive printing layer that has a resistivity lower than about 50 thousand ohms per cubic centimeter and an insulating layer disposed adjacent the conductive layer that has a resistivity of greater than about two megohms per cubic centimeter.
In the invention in accordance with the seventh aspect, the photo-sensitive polymer material may have a concentration of conductive particles dispersed therein to provide the photo-sensitive polymer material with a resistivity in the range between about 50 thousand ohms per cubic centimeter and about 1.5 megohms per cubic centimeter; the insulating layer may comprise an insulating sleeve; the insulating layer may comprise a fiberglass sleeve; the printing structure may have a thickness of less than about one-fourth of an inch; and the semi-conductive printing layer may have a resistivity in the range between about 100 thousand ohms per cubic centimeter and about one megohm per cubic centimeter.
In accordance with a further aspect, the invention is directed to a flexographic printing apparatus for printing a moving web comprising a rotatable ink roller, a roller support that rotatably supports the ink roller, an ink source associated with the ink roller that provides ink to be applied to the ink roller, a rotatable printing roller associated with the ink roller, and a printing plate disposed on the printing roller that is supported so that ink is transferred from the ink roller to the printing plate as the ink roller and the printing roller rotate. The printing plate comprises a semi-conductive printing layer having an image-forming surface and comprising a photo-sensitive polymer material and a substrate layer on which the semi-conductive printing layer is formed. The substrate layer comprises an insulating material having a resistivity of greater than about two megohms per cubic centimeter. The semi-conductive printing layer comprises a plurality of portions of semi-conductive material formed on the substrate layer that are spaced apart and formed so that portions of the substrate layer are not covered by the portions of the semi-conductive material. The apparatus also comprises an insulating layer disposed on the printing roller between an outer surface of the printing roller and the printing plate, a rotatable backing roller disposed adjacent the printing roller so that the moving web to which ink is to be applied passes between the backing roller and the printing plate as the backing roller and the printing roller rotate so that a printed image is applied to the web, and a charge applicator associated with the printing roller that causes an electric charge to be applied to the printing plate. The charge applicator comprises an elongate charge bar having a plurality of charging electrodes spaced from the printing plate, the charging electrodes being evenly spaced from each other in a direction parallel to a central axis of the printing roller, each of the charging electrodes being conductively connected to a voltage.
The features and advantages of the invention will be apparent to those of ordinary skill in the art in view of the detailed description of the preferred embodiment, which is made with reference to the drawings, a brief description of which is provided below.